Trace metal contamination in sediment in the Mhlathuze Estuary, northern KwaZulu-Natal, South Africa: effects on the macrobenthic community

Abstract

Mhlathuze Estuary constitutes one of the ecological most important estuaries in southern Africa and is regarded as an estuary of high conservation importance. The ongoing expansion of the adjacent industrialized Richards Bay Harbour increases the risk of metal pollution to the estuary. This study provides insight into the extent and sources of trace metal contamination using pollution indices and sediment quality guidelines and the effect on macrobenthic habitat quality. Sediment samples for sediment metal and macrobenthic analysis were collected quarterly during 2016-2017 at five sites in the estuary using a marine-grade Zabalocki grab. Metal concentrations were determined using an ICP-OES. Sediment metal concentrations were consistently highest in the subtidal mudflats and lowest in marine sand at the mouth of the estuary. Concentrations of all metals displayed significant differences between sites (P < 0.05). Pollution indices indicated moderate enrichment of Cr at all sites, although the mean pollution load index showed the estuary to be unpolluted. Comparison with sediment quality guidelines revealed that concentrations of Ni and Cr were potentially toxic to biota. Using multivariate analysis, metal concentrations appeared not to significantly affect the macrobenthic community. The multi-metric biotic index M-AMBI proved to be a robust tool in the habitat quality assessment of the estuary. The continuing use of M-AMBI as a biomonitoring tool for ecological management of the estuary is advocated.

Aquatic Ecological Risk of Heavy-Metal Pollution Associated with Degraded Mining Landscapes of the Southern Africa River Basins: A Review

“…SA river systems' physical and chemical water qualities have been extensively documented and used to categorise their ecological statuses [43,62,179]. Heavy-metal pollution in the different aquatic matrices of SA lotic systems has received increasing attention over the past decades due to the associated negative ecological impacts [96,[180][181][182][183]. The pollution intensity and environmental impact of HM contamination will likely increase with the demand for raw materials, advances in industrial mining and processing technologies, and expansion of areal mining in the SA region.…”

Bioaccumulation of trace metals in the ocypodid burrowing crab, Paratylodiplax blephariskios, in Richards Bay Harbour, South Africa

“…It is worth mentioning that the concentration of these metals represents an underestimation of the actual concentrations. A minimum calibration coefficient obtained at 0.999 was deemed acceptable in the evaluation of calibration curves during metal (tissue and sediment) analysis (Izegaegbe et al 2020).…”

“…Despite being one of the largest and busiest ports in South Africa, RBH still serves as a fully functioning and ecologically important estuary, containing large areas of natural estuarine habitat, including intertidal mudflats, sandflats and mangroves. Ongoing port and associated industrial activities resulted in water and sediment contamination in parts of the harbour (Greenfield et al 2011;MER 2013;Izegaegbe et al 2020). Remobilisation of toxic chemicals from contaminated sediments has been highlighted as a major risk associated with dredging operations in harbours (Bocchetti et al 2008;Martins et al 2012).…”